1. Field of the Invention
The present invention relates to an image forming apparatus such as a copy machine or a printer employing an electrophotography method or an electrostatic recording method, and more particularly to an improvement of an image forming apparatus (mainly, effective as an intermediate transfer type image forming apparatus) having a configuration that toner images formed by an image generating engine are transferred on a recording material and then the toner images are thermally fixed by a fixing unit.
2. Description of the Related Art
As one example of conventional image forming apparatuses, there has been known an intermediate transfer type color image forming apparatus in which each color component toner image formed on an image forming carrier such as a photoconductor drum is primarily transferred on an intermediate transfer body sequentially, and multicolor toner images on the intermediate transfer body are collectively transferred on a recoding material such as paper by a secondary transfer unit.
Recently, there has been a keen need of high speed operation, miniaturization, and saving energy for such a color image forming apparatus.
Particularly for the high speed operation of the color image forming apparatus, although a tandem structure where color image forming units for forming color component toner images are arranged in parallel on an intermediate transfer belt is effective, there is a problem in that the color image forming apparatus may become big under such a structure where the color image forming units are arranged in parallel and a fixing unit is placed on the elongation thereof.
As a measure against this problem, for example, as shown in FIG. 10, there has been proposed a technique where an intermediate transfer belt 201 is obliquely arranged, image forming units 202 (202a to 202d) are arranged in parallel along an upper inclined plane of the intermediate transfer belt 201, a collective transfer unit (for example, a collective transfer roll) 203 is arranged at a lower end portion of the intermediate transfer belt 201, and a fixing unit 204 is arranged in a space under the obliquely arranged intermediate transfer belt 201, (for example, see Japanese Patent No. 3470696).
According to the above mentioned technique, since the dimension in the width direction of the image generating engine (the image forming units 202 and the intermediate transfer belt 201) is suppressed, the fixing unit 204 is arranged under the image generating engine, and the image forming units 202 are not arranged in parallel to the fixing unit 204, the dimension in the width direction of the image forming apparatus can be set to be short, thus allowing the implementation of a miniaturized image forming apparatus.
However, according to such a conventional image forming apparatus, since the fixing unit 204 is arranged under the image generating engine, heat generated from the fixing unit 204 when it operates for a long time has an influence on the image forming units 202 located above the fixing unit 204. This may lead to deterioration of image quality, such as toner fusion due to the heat, in the image forming units 202. In order to overcome this problem, it is necessary to arrange a heat reflection plate 205 between the fixing unit 204 and the intermediate transfer belt 201 or to provide an exhaust system (not shown) such that the heat generated from the fixing unit 204 is not moved to the image forming units 202. As a result, the structure of the image forming apparatus is more complicated.
As mentioned above, when the heat reflection plate 205 or the exhaust system is used, since some of energy used for the fusion by the fixing unit 204 is exhausted to the outside, thermal energy efficiency of the fixing unit 204 is apt to be insufficient.
In addition, for such a conventional color image forming apparatus, a recording material supply tray (not shown) is commonly disposed under the image generating engine in respect that a recording material 206 passes through the collective transfer unit 203 located at the lower end portion of the image generating engine and the fixing unit 204 located under the image generating engine. In this case, since the recording material supply tray is disposed near a lower portion of a case body of the image forming apparatus, and therefore, a user must crouch or stoop down when he replenishes the recording material supply tray with the recording material, thus giving him an inconvenience.
There has been conventionally proposed another image forming apparatus in which the image generating engine and the fixing unit are disposed in a lower region within the image forming apparatus case body, an upper recording material supply tray is disposed in an upper region within the image forming apparatus case body, and the recording material is introduced from the upper recording material supply tray into the image generating engine and the fixing unit through a roughly S-shaped carrying path (for example, see JP-A-4-274264 (embodiments, FIG. 1)).
With this apparatus, while standing, a user can more easily replenish the upper recording material supply tray with the recording material since the upper recording material supply tray is disposed at the upper portion of the image forming apparatus case body.
However, in this apparatus, since the S-shaped carrying path of the recording material extends long from the upper recording material supply tray to the image generating engine and the fixing unit, time taken until output of the recording material (First Copy Output Time: FCOT) from an initial image generating operation is prolonged, and, moreover, the fixing unit is unavoidably disposed near the image forming apparatus case body. Accordingly, the heat generated from the fixing unit is apt to exhaust to the outside of the image forming apparatus, which results in much heat loss and hence a poor energy efficiency of the fixing unit.
Since most of the heat generated from the fixing unit is exhausted to the outside of the image forming apparatus, the disposition location of the upper recording material supply tray does not reach a region immediately above the fixing unit, and the fixing unit is very distant from the upper recording material supply tray, it is not nearly expected that the heat generated from the fixing unit preliminarily heats the recording material within the upper recording material supply tray. On this account, heat of the fixing unit is much dispossessed by the recording material in a fusing process by the fixing unit, thus resulting in increase in energy consumption of the fixing unit.